In the mobile communication system, due to the time-varying characteristic of the wireless fading channel, the communication process has a lot of uncertainties, and on one hand, in order to improve the system throughput, a high-order modulation and a low redundancy error correcting code with a relatively high transmission rate are used for the communication, therefore the system throughput indeed improves significantly when the signal to noise ratio of the wireless fading channel is relatively ideal, however, when the channel is in deep fading, it cannot guarantee a reliable and stable communication, and on the other hand, in order to ensure reliability of the communication, a low order modulation and a high redundancy error correcting code with relatively low transmission rate are used for the communication, that is, it ensures a reliable and stable communication when the wireless channel is in deep fading, however, when the signal to noise ratio of the channel is relatively high, due to a relatively low transmission rate, the increase of system throughput is restricted, thereby resulting in a waste of resources, and in the early development of mobile communication technology, people fights the wireless fading channel time-varying characteristic only by increasing the transmission power of the transmitter and using a low-order and large redundancy modulation and coding method to ensure the communication quality of the system when the channel is in deep fading, and how to increase the system throughput has not been considered, and along with improvement in technology, there has appeared technology which adaptively adjusts its transmission power, modulation and coding scheme and data frame length based on the channel state to overcome the channel time-varying characteristic, so as to obtain the best communication effect, and the technology is known as adaptive coding and modulation technology, which is the most typical link adaptation technology.
In the Long Term Evolution (LTE) system, the control signaling which needs to be transmitted in the uplink has Acknowledgement/Negative Acknowledgement (ACK/NACK), and three forms which reflect the channel state information (CSI) of the downlink physical channel: channel quality indication (CQI), Pre-coding Matrix Indicator (PMI), and Rank Indicator (RI).
The CQI is an index used to measure the quality of the downlink channel. In the 36-213 protocols, the CQI is indicated with values of integers from 0 to 15, which respectively represent different CQI levels, and different CQIs correspond to respective Modulation and Coding Schemes (MCS), see Table 1. The CQI grade selection should follow the following guidelines:
TABLE 1CQI indexModulationCode rate × 1024Efficiency0out of range1QPSK780.15232QPSK1200.23443QPSK1930.37704QPSK3080.60165QPSK4490.87706QPSK6021.1758716QAM3781.4766816QAM4901.9141916QAM6162.40631064QAM4662.73051164QAM5673.32231264QAM6663.90231364QAM7724.52341464QAM8735.11521564QAM9485.5547
The Quadrature Amplitude Modulation (QAM) in Table 1 represents the quadrature amplitude modulation, and the Quadrature Phase Shift Keying (QPSK) represents the quadrature phase shift keying which is a digital modulation scheme.
The selected CQI level should be such that the block error rate of the Physical Downlink Shared Channel (PDSCH) transport blocks corresponding to the CQI under the corresponding MCS does not exceed 0.1.
Based on one non-limiting detection interval between the frequency domain and the time domain, the User Equipment (UE) will obtain the highest CQI value which corresponds to each maximum CQI value reported in the uplink subframe n, and the CQI index is in the range of 1-15, and meets the following condition, and if the CQI index 1 does not meet the condition, the CQI index is 0: the error rate of a single PDSCH transport block does not exceed 0.1 when being received, the PDSCH transport block comprises joint information: modulation scheme and transport block size, which corresponds to one CQI index and a group of occupied downlink physical resource blocks, that is the CQI reference resource. Wherein, the maximum CQI value is the maximum CQI value when ensuring that the Block Error Ratio (BLER) is not greater than 0.1, and it helps to control the resource allocation. Generally, the smaller the CQI value is, more resources will be occupied, and the BLER performance is better. For the joint information corresponding to one CQI index and having the transport block size and modulation scheme, if: the joint information transmitted by the PDSCH in the CQI reference resource according to the related transport block size can be notified with signaling, in addition:
the modulation scheme is characterized with the CQI index and uses the joint information including the transport block size and the modulation scheme in the reference resource, and the effective channel coding rate generated by the modulation scheme is the most closing effective channel coding rate which can be characterized with the CQI index. When there is more than one of the joint information and all of the join information can generate similarly closing effective channel encoding rate characterized by the CQI index, the joint information having the minimum transport block size is used.
Each CQI index corresponds to one modulation scheme and transport block size, and the corresponding relationship between the transport block size and the number of physical resource blocks (NPRB) can be showed with a table. The coding rate can be calculated according to the transport block size and the NPRB.
In the LTE system, the ACK/NACK is transmitted on the physical uplink control channel (PUCCH) in the PUCCH format 1/1a/1b, if the User Equipment (UE) needs to transmit uplink data, the data are transmitted on the physical uplink shared channel (PUSCH), the CQI/PMI, RI feedback may be a periodic or a periodic feedback, and the specific feedback is shown in Table 2:
TABLE 2uplink physical channels corresponding to periodic feedbackand a periodic feedbackPeriodic CQIAperiodic CQIScheduling patternreport channelreport channelFrequency non-PUCCHselectiveFrequency selectivePUCCHPUSCH
Wherein, for the periodic CQI/PMI, RI feedback, if the UE does not need to transmit the uplink data, the periodic CQI/PMI, RI feedback is transmitted on the PUCCH in PUCCH format 2/2a/2b, if the UE needs to transmit the uplink data, the CQI/PMI, RI is transmitted on the PUSCH; the aperiodic CQI/PMI, RI feedback is only transmitted on the PUSCH.
The Long-Term Evolution (referred to as LTE) Release 8 standard defines the following three downlink physical control channels: Physical Control Format Indicator Channel (referred to as PCFICH), Physical Hybrid Automatic Retransmission Request Indicator Channel (referred to as PHICH) and Physical Downlink Control Channel (referred to as PDCCH). Wherein the PDCCH is used to carry Downlink Control Information (referred to as DCI), comprising: uplink, downlink scheduling information, and uplink power control information. The DCI format is divided into the following: DCI format 0, DCI format 1, DCI format 1A, DCI format 1B, DCI format 1C, DCI format 1 D, DCI format 2, DCI format 2A, DCI format 2B, DCI format 2C, DCI format 2D, DCI format 3, and the DCI format 3A, and the like;
In the LTE, downlink control information such as the coding and modulation scheme, the resource allocation position and the HARQ information need to be defined in the downlink control signaling. Wherein, the downlink scheduling of the base station determines the coding and modulation scheme, and especially, the protocol defines a modulation and transport block size table, and each row of the table corresponds to one MCS index, for each MCS index, the modulation and transport block size table defines one combination of modulation scheme and code rate, and the specific table can refer to the LTE 36.213 standard, and one MCS index essentially corresponds to one spectral efficiency, the selection for the MCS index needs to refer to the desired CQI value, generally the base station needs to consider the spectral efficiencies of the two parties in the implementation. The base station determines the MCS index and also needs to determine the resource allocation information, and the resource allocation provides the number of physical resource blocks (NPRB) which need to be occupied in the downlink transmission, the LTE standard also provides a transport block size (TBS) table, and the table defines the TBS size under the condition of a given MCS index and the number of physical resource blocks (NPRB), and with these coding and modulation parameters, the downlink coding and modulation can be performed.
In Release 10 (R10), the UE is semi-statically configured to receive the PDSCH data transmission through the high-layer signaling based on one of the following transmission modes and according to the PDCCH indication of UE-Specific search space:
Transmission Mode 1: Single-antenna port; port 0
Transmission Mode 2: Transmit diversity
Transmission Mode 3: Open-loop spatial multiplexing
Transmission Mode 4: Closed-loop spatial multiplexing
Transmission Mode 5: Multi-user MIMO
Transmission Mode 6: Closed-loop Rank=1 precoding
Transmission Mode 7: Single-antenna port; port 5
Transmission Mode 8: dual-stream transmission, namely double-stream beamforming
Transmission Mode 9: Up to 8 layer transmission
Transmission Mode 10: up to 8 layer transmission which supports the COMP function.
After experiencing several versions such as R8/9/10, the Long Term Evolution (referred to as LTE) system gradually and accurately studied the R11 technology. At present, some R8 products began to gradually become commercial, the R9 and the R10 are to be further product planned.
A modulation and coding scheme of up to 64QAM is supported in the uplink and downlink in the existing standards, and along with the development of heterogeneous networks, the small cell requires higher data transmission rate and higher system spectral efficiency, but the existing standards cannot meet this requirement.